Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$215.99	12.505%	$242.9995	$243.00	$243.00	$243.00
Purchase #2	$86.56	5.279%	$91.1295	$91.13	$91.15	$91.10
Purchase #3	$209.60	11.223%	$233.1234	$233.12	$233.10	$233.10
Purchase #4	$95.25	7.506%	$102.3995	$102.40	$102.40	$102.40
Purchase #5	$130.38	9.123%	$142.2746	$142.27	$142.25	$142.30
Purchase #6	$66.84	8.744%	$72.6845	$72.68	$72.70	$72.70
Purchase #7	$166.75	4.418%	$174.117	$174.12	$174.10	$174.10
7 purchase totals =	$971.37		$1,058.7280	$1,058.72	$1,058.70	$1,058.70